1. File of the Invention
This invention is directed to various members of a gene family with transformation modulating activity, and to diagnostic and gene therapy techniques based an the variants.
2. Review of Related Art
Prostatic adenocarcinoma is the most frequent malignancy in adult men with approximately 317,000 new cases diagnosed each year (Parker, et al., CA, 46:8-27, 1996). In spite of the capabilities for early diagnosis and treatment (Potosky, et al., JAMA, 273:548-552, 1995), it represents the second leading cause of cancer death in men following lung cancer.
To date, the study of alterations in specific genes has not been particularly rewarding in primary prostate cancer. Most alterations in the widely studied oncogenes and tumor suppressor genes occur in only 20-30% of primary prostate carcinomas, except for the myc gene, where overexpression has been observed in as many as 50-60% of such cases (Fleming, et al., Cancer Res., 46:1535-1538, 1986). Up to 40% of primary prostate cancers studied by comparative genomic hybridization display chromosomal aberrations (Visakorpi, et al., Cancer Res., 55:342-347, 1995), although such alterations occur more frequently as tumors recur and become refractory to hormonal therapy. Characterization of candidate proto-oncogenes or tumor suppressor genes at such altered loci may eventually shed light on tumor progression in the prostate.
pp32 (GenBank HSU73477) is a highly conserved nuclear phosphoprotein. Increased expression of pp32 or closely related species is a frequent feature of clinical cancers. For example, in human prostate cancer, high-level expression of RNA hybridizing with pp32 probes occurs in nearly 90% of clinically significant prostate cancers, in contrast to the substantially lower frequencies of alterations of other oncogenes and tumor suppressors (See U.S. Pat. No. 5,726,018, incorporated herein by reference).
Molecular Features and Activities of pp32.
pp32 is a nuclear phosphoprotein that is differentiation-regulated during differentiation of adult prostatic epithelium (Walensky, et al., Cancer Res. 53:4720-4726, 1993). The human pp32 cDNA sequence (Gen-Bank U73477) is 1052 bp in length and encodes a protein of 249 amino acids. The protein is composed of two domains: an amino terminal amphipathic α-helical region containing a leucine zipper, and a highly acidic carboxyl terminal region. The murine and human forms of pp32 are highly conserved with over 90% nucleic acid homology and over 95% protein-level homology.
Human pp32 has been isolated independently by a number of groups. Vaesen et al. (“Purification and characterization of two putative HLA class II associated proteins: PHAPI and PHAPII.” Biol. Chem. Hoppe-Seyler., 375:113-126. 1994) cloned an essentially equivalent molecule, termed PHAPI, from an EBV-transformed human B-lymphoblastoid cell line; PHAPII, cloned by the same strategy, is unrelated to pp32. This study identified PHAPI through its association in solution with human HLA class II protein, noting membrane and cytoplasmic localization as well as nuclear; the gene has putatively been localized to chromosome 15q22.3-q23 by fluorescent in situ hybridization (Fink, et al., “Localization of the gene encoding the putative human HLA class II-associated protein (PHAPI) to chromosome 15q22.3-q23 by fluorescence in situ hybridization.” Genomics, 29:309-310,1995). More recently, a group studying inhibitors of protein phosphatases identified pp32 as IIPP2a an inhibitor of protein phosphatase 2a (Li, et al., “Molecular Identification of II PP2A, a novel potent heat-stable inhibitor protein of protein phosphatase 2A.” Biochemistry 35:6998-7002, 1996); another phosphatase inhibitor, I2PP2a, is unrelated to pp32. Interestingly, another recent report (Ulitzur, et al., “Biochemical characterization of mapmodulin, a protein that binds microtubule-associated proteins.” Journal of Biological Chemistry 272:30577-30582, 1997) identified pp32 as a cytoskeletally-associated cytosolic protein in CHO cells. It is not clear whether this finding stems from a difference in system, or whether pp32 can localize to the cytoplasm under certain circumstances, pp32 has also been identified as LANP, a leucine rich nuclear protein in the central nervous system (Matsuoka, et al., “A nuclear factor containing the leucinc-rich repeats expressed in murine cerebellar neurons. Proc Nail Acad Sci USA 91:9670-9674, 1994).
There are also a number of reports of gene products bearing lesser degrees of homology to pp32. The Vacsen group has identified a series of unpublished sequences, termed PHAP12a (EMBL Locus HSPHAP12A) and PHAP12b (EMBL Locus HSPHAP12B), also cloned from an EBV-transformed human B-lymphoblastoid cell line. These variant pp32 sequences are distinct from the sequences reported herein, representing the April protein instead. April, cloned from human pancreas, is shorter than PHAP12a by two N-terminal amino acids (Mencinger, et al., “Expression analysis and chromosomal mapping of a novel human gene, APRIL, encoding an acidic protein rich in leucines.” Biochimica et Biophysica Acta. 1395:176-180, 1998, see EMBL Locus HSAPRIL), PHAP12b is identical to a subset of APRIL. Silver-stainable protein SSP29 (unpublished GenBank Locus HSU70439) was cloned from HeLa cells and is identical to PHAP12a.
The nuclear phosphoprotein pp32 has been linked to proliferation. Malek and associates reported that various neoplastic cell lines showed markedly elevated expression levels and that bacterial polysaccharide induced expression of pp32 epitopes by B lymphocytes upon polyclonal expansion (Malek, et al., J. Biol. Chem., 265:13400-13409, 1990). Walensky and associates reported that levels of pp32 expression, measured by in situ hybridization, increased in direct relation to increasing Gleason grade of human prostatic cancers.
pp32 cDNA probes hybridize strongly with prostatic adenocarcinoma, whereas the hybridization signal in normal prostate is confined to basal cells. Polyclonal,anti-pp32 antibodies react strongly with sections of human prostatic adenocarcinoma. The antibodies and riboprobes used by the investigators in previous studies are consistent with cross-reactivities of the reagents with all reported members of the pp32 nuclear phosphoprotein family, therefore, while previous descriptions focused upon pp32, it cannot be excluded that homologous proteins were detected.